docs: def last_post_on(self):
          """ Returns the latest post date associated with the node or one of its descendants. """
          dates = [n.last_post_on for n in self.children if n.last_post_on is not None]
          children_last_post_on = max(dates) if dates else None
          if children_last_post_on and self.obj.last_post_on:
              return max(self.obj.last_post_on, children_last_post_on)
          return children_last_post_on or self.obj.last_post_on